This is an explainer, not investment advice. It describes common frameworks and their limits so you can think the question through.
The number you keep hearing
Ask how much you need to retire and the first answer is usually a multiple of your spending: 25 times your annual expenses, also expressed as the 4% rule. They are two sides of one coin. If you withdraw 4% of your savings in the first year and adjust that dollar amount for inflation each year after, a pot worth 25 times that first withdrawal is exactly what funds it.
The 4% figure comes from a 1994 study by financial adviser William Bengen, who tested withdrawal rates against U.S. market history back to 1926 and found a retiree could survive even the worst 30-year stretch by starting at roughly 4%. The 1998 "Trinity study" by three finance professors broadly agreed: a 4% initial withdrawal from a 50/50 stock-and-bond portfolio survived virtually every 30-year historical period, as the research is summarized. The "safe withdrawal rate" is the percentage you can take in year one and keep taking, inflation-adjusted, with a high chance of not running out.
Why the debate never settles
Those studies rest on U.S. market history, which has been unusually generous. Critics argue that projecting it forward — with high stock valuations and lower bond yields today — is optimistic. Morningstar's recent research has put a safe starting rate closer to about 3.9% for a balanced portfolio, while Bengen himself has since suggested a higher figure using a broader mix of assets. The spread of expert opinion, very roughly 3.5% to 4.7%, shows how much the answer depends on assumptions about future returns.
A key hazard is sequence-of-returns risk: a run of bad market years early in retirement can do lasting damage even if long-run average returns turn out fine, because selling investments to live on during a slump locks in losses and leaves less to recover. It is why a portfolio packed with volatile stocks does not necessarily support a higher withdrawal rate.
The income-replacement approach
A different lens is the replacement ratio — the share of your pre-retirement income you'll need to keep up your standard of living, conventionally put at 70% to 80%. The idea is that in retirement you stop saving for retirement, payroll taxes fall, and work costs disappear, so you need somewhat less than your final salary.
Fidelity frames it in savings milestones: aim for roughly 1x your salary saved by 30, 3x by 40, 6x by 50, and about 10x by 67 — with savings replacing around 45% of pre-retirement income and Social Security and any pension covering the rest. How much must come from your own savings varies with income: because Social Security replaces a larger share of a lower earner's wages, higher earners generally have to cover more of their retirement from personal savings.
Where Social Security fits
Social Security is central, not a footnote. The Social Security Administration reports the average retired-worker benefit in 2025 at about $1,907 a month — roughly $22,900 a year — and the program is designed to replace around 40% of an average earner's income (more for lower earners, less for higher ones).
When you claim matters a lot. Benefits rise for each year you delay between 62 and 70, so a later claim means more guaranteed, inflation-linked income for life — which directly shrinks the amount your own savings must cover.
The costs the rules understate
Two expenses tend to outrun general inflation. Health care is the first: Fidelity's 2025 estimate puts the average lifetime health-care cost for a 65-year-old retiree at about $172,500 — a figure that has more than doubled since the early 2000s — because premiums, deductibles and uncovered items like dental and vision add up even with Medicare.
Longevity is the second. The 30-year horizon baked into most safe-withdrawal research assumes living to 95 if you retire at 65, and a meaningful share of 65-year-olds — especially women, and at least one member of a couple — live beyond 90, according to the SSA's actuarial tables. A pot built to last 30 years may need to last longer.
A process beats a number
Every rule above is a simplification — handy for a sanity check, risky as a final plan. The 4% rule assumes a particular asset mix, a 30-year horizon and U.S. returns; the 80% replacement ratio assumes your spending tracks your old salary. Neither knows your mortgage, your health, your taxes or your partner's income.
The value of these frameworks is less the number they spit out than the thinking they force. Working backward from what you actually expect to spend, counting the guaranteed income you can rely on, and stress-testing the result against a bad market, a health shock or a longer life tends to produce a more honest — and more durable — answer than any single figure. For most people, that answer is a range, revisited regularly, not a magic number.
